Solar cell

ABSTRACT

Proposed is a silicon solar cell with a substrate body on one side of which an electrical field is generated by an MIS contact to cause separation of charge carriers generated by radiation energy. The minority charge carriers are drawn off in the metal of the MIS contact, whereas the majority charge carriers are conducted away by ohmic contacts arranged on the opposite side. The ohmic contacts are located on elevated areas relative to the substrate surface. Moreover, the side of the substrate body bearing the ohmic contacts is completely covered with at least one passivation layer.

BACKGROUND OF THE INVENTION

The invention relates to a solar cell, especially to a thin-film solarcell of semiconductive material such as silicon, in whose semiconductivesubstrate minority and majority charge carriers are generated byradiation energy, said charge carriers being separatable by an electricfield and thus dischargeable, with ohmic contacts being arranged atintervals on a (first) semiconductive substrate surface and interlinked,with a passivation layer arranged at least between the ohmic contacts,said passivation layer preferably also covering the ohmic contacts.Furthermore, the invention relates to a method of producing a solarcell.

By structuring an appropriate solar cell, it is possible to reducerecombination of charge carriers in the vicinity of the ohmic contactswithout having to generate a potential threshold for minority chargecarriers through alloying, diffusion or ion implantation in thesemiconductive substrate.

SUMMARY OF THE INVENTION

The object of the present invention is therefore to structure a solarcell of the type described at the outset, such that the thickness of thesemiconductive substrate can be significantly reduced without involvingthe risk of increased recombination in the vicinity of the ohmiccontacts. Moreover, in spite of reducing the thickness of thesemiconductive material, recombination in the vicinity of the ohmiccontacts must be considerably reduced, whereby isolation of the chargecarriers from the ohmic contacts must not necessarily be achieved bymeans of a potential barrier.

The invention solves the task in that the electrical field separatingthe minority and majority charge carriers flows in the region of a(second) semiconductive substrate surface is located opposite thatsubstrate body surface having the ohmic contact zones, so that themajority charge carriers diffuse to the ohmic contact zones and arecollected by them, and that said ohmic contacts are arranged on firstzones or areas of the first semiconductive substrate surface, which onthe opposite side are elevated in relation to the second zones or areasof the semiconductive substrate existing between the ohmic contacts.

In accordance with the principles of the invention, the ohmic contactsserve to collect the majority charge carriers, and are applied directlyonto the substrate material without a doped intermediate film (i.e.,without special screening by means of a potential barrier). Due to theabsence of a potential barrier, minority charge carriers in addition tomajority charge carriers can also always penetrate to the ohmiccontacts, although when said minority charge carriers behave ideallyrelative to the isolating electrical field they should diffuse to theohmic contacts on the opposite side. However, in order to reducerecombination of majority and minority charge carriers in the region ofthe ohmic contacts, the invention proposes that the ohmic contactsshould be applied elevated e.g., as narrow strips, relative to theirsurroundings, said surroundings being very well passivated with aninsulating lamina. This arrangement ensures that the distance betweenthe ohmic contacts and the opposite side collecting the minoritycarriers is relatively great, even in the case of very thinsemiconductive substrates, and preferably greater than the diffusionlength of the minority charge carriers, so that only few minority chargecarriers can reach the ohmic contacts (low concentration gradienttowards the ohmic contacts). The primary difference in the present stateof the art can be recognized herein, even though elevated formation ofthe ohmic contacts is already known as disclosed in e.g.,US-A-4,322,571, US-A 4,367,368 or US-A-4,135,950. However, the ohmiccontacts in the solar cells described therein are screened by apotential barrier. The ohmic contacts are not deposited directly ontothe semiconductive substrate. Moreover, there is no passivation layerbetween the ohmic contacts. Finally, according to the state of the art,the ohmic contacts do not have the task of improving the stability ofthin-film solar cells, that is cells with a substrate thickness so thinthat they would be in danger of fracturing.

In other words, according to the invention, it is proposed that theohmic contacts be spatially separated from the remaining semiconductivesurface, said surface being very well passivated by a passivation layer(insulating lamina). This measure allows the choice outside the ohmiccontacts of a semiconductive substrate thickness less than the diffusionlength of the minority charge carrier, so that a higher solar cellefficiency can be achieved. Note, however, that the recombination in thevicinity of the ohmic contact is not increased, since in this area theseparation distance from the opposite side of the semiconductivesubstrate is preferably considerably greater than the diffusion lengthof the minority charge carrier.

Structuring of the semiconductive surface with the ohmic contacts ispreferably achieved by selective etching. In doing so one commences withan appropriately thick semiconductive wafer, which is preferably thickerthan the diffusion length of the minority charge carrier. This havingbeen done, one defines the ohmic contact areas so as to cover them witha suitable etching mask. The areas not covered by the etching mask arethen etched away to leave the required thickness of semiconductivesubstrate. Insofar as the etching mask is not simultaneously formed bythe metal of the ohmic contacts--which point represents a furtherinnovative feature--said etching mask is subsequently removed, so as toapply the metal of the ohmic contact as appropriate. Examples ofsubstances for etching masks are photo-sensitive resist, SiO₂ or Si₃ N₄.It is also possible for the metal to be beneath the etching mask.

The etching agent itself can be of the isotropic or anisotropic,chemical or plasma, ion, reactive ions or laser variety. Anisotropicetching agents are particularly advantageous when a (100)-orientatedsilicon is used because, as is known, the (100)-surface is etchedconsiderably faster than the (111)-surface. In this case underneath theetching mask are the trapezoidal section areas with an edge angle of54.7°. The ohmic contacts are then mounted on the peaks, i.e., the outerfaces of these areas. Worthy of particular consideration as anisotropicetching agents are the known structure etchers on the basis of, e.g.,potassium hydroxide or ethylene diamine. It is also possible to makeadvantageous use of (110)-surfaces in conjunction with anisotropicetchers, whereby elevated areas defined by perpendicular walls areproduced. A rectangular cross-section results.

As previously mentioned, as proposed in the invention, the ohmiccontacts serve simultaneously as etching masks. Simultaneously with theetching procedure, the uncovered areas are textured to enhance thepenetration of light into the Si surface passivated with the insulatinglamina.

With respect to the metals used in the actual ohmic contact, it must benoted that these can be applied, e.g., by thermal vapour depositing in avacuum through a mechanical mask, by screen printing, through cathodesputtering, and structured by photolithographic means if required.

The areas elevated for the ohmic contacts additionally provide anadvantage in that they increase the strength of the semiconductivesubstrate without the risk of susceptibility to fracture, even thoughthe film thickness is certainly small between the elevated portions.This factor plays a big role particularly when an inexpensive single-and polycrystalline (`solar grade`) silicon material with a shortdiffusion length is used for the minority charge carriers.

This allows, amongst other things, this material to also exploit theradiation impinging on the rear of the solar cell.

A further advantage embodied in the form of the solar cell of theinvention is that contacting thin solar cells, for example by ultrasonicwelding, is made substantially easier in that it is done on the thicksemiconductive area covered by the ohmic contacts, or else on anadditional contact area consisting of thick semiconductive materialformed on the edge simultaneously with the etching of the ohmic contactzone, and without the risk of any breakage in the thin silicon areas.Furthermore, this arrangement with a passivation layer extending beyondthe lateral edge of the solar cell allows the front-surface contact tobe led over the edge to the rear where it is contacted. Contacting bothconnections on one side, e.g., by ultrasonic welding, considerablysimplifies the production process.

The solar cell construction proposed in the invention can be used forsingle- and polycrystalline silicon as well as for compoundsemiconductors.

Further details of the invention can be seen from the claims, and fromthe features to be found therein individually and/or in combination.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details, advantages and features of the invention can be seenfrom the following description of preferred designs as illustrated inthe drawing.

The illustrations show the following:

FIG. 1 shows a first embodiment of a silicon solar cell according to theinvention having ohmic contacts on the front surface,

FIG. 2 shows a silicon solar cell having ohmic contacts on the rearsurface, and

FIG. 3 shows a further embodiment of a silicon solar cell having ohmiccontacts on the rear surface.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates an embodiment of solar cell (19) constructedaccording to the invention, said solar cell comprising a p-doped siliconsubstrate as the body (1), a thin silicon oxide layer (2), ohmiccontacts (4) and an MIS (metal-insulator-semiconductor) contactconsisting of the p-silicon of the silicon body (1), the silicon oxidelayer (2) and the metallized layer (3) preferably of aluminum ormagnesium or a double layer of Mg/Al.

The ohmic contacts (4) are discontinuously arranged on thesemiconductive substrate (1) whereby, according to the invention, saidcontacts are arranged on the exposed front surfaces (31) of elevations(21). Said arrangement ensures that the distance between the ohmiccontacts and the opposite side (27) of the semiconductive substrate (1)is greater than in the remaining surface area of the semiconductivesubstrate (1), said surface area being designated (22) in the drawing.Together with the underlying elevated silicon zones (21), the ohmiccontacts (4) can form a geometric pattern described as interconnectedstrips, rings or dots. In other words, the silicon zones (21) with theohmic contacts (4) could exhibit a comb, grid or ring structure whenviewed in plan. Thereby, the ring structure could be formed byconcentric rings with radially running paths.

Passivation layers extend between the elevated ohmic contact zones (4),being composed on the one hand of the silicon oxide layer (2) grownnaturally or else generated below 800° C., and a further insulatinglamina (5), which can serve as a passivation layer and as ananti-reflection layer. The thickness of the upper, designated the firstpassivation layer (5) can thereby be approx. 80 nm, and comprisespreferably of aluminium oxide or silicon nitride. The further insulatinglamina, designated the second passivation layer, in the form of thesilicon oxide layer (2), can be built up differently on the front andrear surfaces of the silicon substrate (1). It is therefore possible tovary the thickness within wide limits, since said layer does not act asa tunnel insulator. It is naturally also possible to dispense with saidlayer completely.

Both the natural silicon oxide layer and a silicon oxide layer (2),specially prepared for example by thermal or other oxidation methods,can be used for interfacial passivation. By natural silicon oxide layeris meant that film which is always present on the silicon substrate (1)and which is only a few atom layers thick.

The structural composition of the silicon oxide layer (2) itself can bechanged on the front surface by the subsequent deposition of the firstpassivation layer (5), e.g., silicon nitride. A conversion of siliconoxide into silicon oxynitride is therefore possible, for example.

Unlike in conventional solar cells, the charge carriers primarilygenerated near the front by the incident light must first diffusethrough the whole substrate (1), so as to be collected by the MIScontact on the rear. It is hereby extremely important for the frontside, comprising the silicon surface in the zones around the ohmiccontacts (4) and those covered by the passivation layers (2) and (5), tohave a low surface recombination speed, since otherwise a largeproportion of the charge carriers will prematurely recombine there.

According to the invention, a silicon etching process effectivelyelevates the ohmic contacts (4) above the top surface, therebyeliminating their recombination flow to a greater or lesser extentaccording to the height the zones. This is because this measureconsiderably increases the distance of the ohmic contacts (4) both fromthe point at which the charge carriers are generated in the siliconvolumes (1) and from the collecting MIS contact (3), so that as a resultof the now increased concentration gradient the minority charge carriersdiffuse in preference to the MIS contact where they are utilized. Forreasons of advantage, the distance from the ohmic contacts (4) (surface(31)) to the MIS contact (3) on the opposite side (surface (27)) shouldbe greater than the diffusion length of the minority charge carriers.The thickness of the silicon substrate (1) in area (22) can be greater,equal to or smaller than the diffusion length, but preferablysubstantially smaller. However, insofar as the thickness is indeedsubstantially smaller than the diffusion length, as many as possible ofthe minority charge carriers generated on the front surface can diffuseto the rear surface without recombining.

According to the invention, this optimization of the substrate thicknessand the height of the ohmic contact zones can be achieved independentlyfrom one another through suitable choice of the initial thickness of thesilicon layer and through the duration of the etching process. A furtheradvantage results from the elevated silicon ridges (21) below the ohmiccontacts (4) serving as mechanical reinforcement for the silicon mass(1). Said mass must be as thin as possible (down to 10 μm) in order toensure high efficiency, particularly for cheap solar silicon (shortdiffusion length); said arrangement not being achievable without themechanically strong ohmic contact zone, at least not over large areas.Said arrangement makes possible the production of solar cells onextremely thin silicon, including on a large industrial scale.Furthermore, texturing of the silicon surface to increase the incidentlight can be done simultaneously with the etching process (anisotropicetching).

The ohmic contacts (4) are preferably arranged in the form of fingers,i.e., they comprise ridges running in parallel to one another, andlinked on one side (comb-form). The distances between the ohmic contactfingers must be significantly greater than the thickness `d` (distancebetween surfaces (22) and (27)) of the silicon substrate (1) and thediffusion length of the minority charge carriers, so that the mean pathto the collecting MIS contact is less than to the ohmic contact zone.The maximum distance between the ohmic contacts (4) is limited by theseries resistance. The optimum distance is in the range from 1 to 5 mm,the finger width in the range 50 to 300 μm, thereby achieving a contactsurface proportion or shading effect of less than 10%.

The rear surface metal (3) of the MIS contact serves as a reflector forthe unabsorbed light, thereby considerably increasing both the lightpath in the silicon and the generation of charge carriers, which featureparticularly facilitates advantageous utilization of very thin,inexpensive solar silicon. Moreover, reflection of the infra-redcomponent of the sunlight on the rear leads to less heating of the solarcell, and consequently to higher efficiency under real operatingconditions. With respect to the elevated silicon zones (21), it shouldbe mentioned that their cross-sections could be trapezoidal, rectangularor curved.

FIGS. 2 and 3 illustrate further embodiments of solar cells (20) and(30) respectively, that comply with the principles of the invention. Inboth cases the ohmic contact (10) or (16) respectively is arranged onthe rear surface of solar cell (20) or (30), and directly on thesemiconductive substrate body (6) or (12) and likewise in certain areas,as was the case in FIG. 1.

The solar cell shown in FIG. 2 corresponds to the basic design principleof the silicon nitride inversion-layer solar cell with MIS contactsdescribed in DE-PS 28 40 096. The solar cell (20) thus has a p-dopedsilicon substrate or body (6) upon which is arranged a thin siliconoxide layer (7). Arranged on the front surface are MIS contactscomprising the semiconductive substrate (6), the silicon oxide layer (7)and discontinuous metal layers (8) preferably arranged in strips. Afurther insulating layer (9), preferably comprising silicon nitride,extends over the surface comprising the areas of silicon oxide layer (7)and the metal strips (8). A stationary positive surface charge,comprising the natural charges and those introduced by foreign ions,must be located in said silicon nitride layer (9) on the nitride-oxidejunction; said charge induces on the surface of the p-doped siliconsubstrate (6) an inversion layer comprising electrons. The electrons(minority charge carriers) generated by the light diffuse towards thefront where they are accelerated in the electrical field generated bythe positive insulator charges, and travel along the highly conductiveinversion layer to the MIS contacts, through which they leave thesilicon body (6) and pass into an external circuit. The majority chargecarriers, i.e., holes in the p-doped silicon body (6), diffuse towardsthe ohmic contacts (10).

Further provided is an additional passivation layer (11) also coveringthe ohmic contacts (10). As the decisive feature, attention is drawn tothe elevated arrangement of the ohmic contacts (10), i.e., to theprojections (23) preferably in strip form elevated relative to thenormal top surface (24), said projections being formed by a siliconetching process. This arrangement strongly reduces the influence of theohmic contacts (10) on recombination of the charge carriers, andcompletely eliminates it where the distances from the points of originare considerably greater than the diffusion length. This in turn allowsthe actual silicon substrate (6) to be made thinner without increasingrecombination, thereby substantially increasing the level of efficiencyrelative to the incident light both from the front and from the rear.

Of particular significance here too is the decisive advantage that themechanical strength of the thin silicon substrate (6) is considerablyenhanced by the silicon elevations or bracing ridges (23) beneath theohmic contacts (10); said advantage therefore enabling for the firsttime the economic production of high-efficiency extremely thin (d˜50 μm)silicon solar cells, which can be illuminated from both sides. It mustbe particularly noted that the above can be achieved essentially withoutmore technical effort.

In this case also, use of an anisotropic etching medium and (100)- or(110)-orientated silicon, makes it possible to texture the rear surfaceat the same time as etching the contact zones (10). The spaces betweenthe MIS contacts on the front side (50 μm-1 mm) are substantially lessthan the spaces between the ohmic contacts (10) on the rear (1 mm-5 mm).The distance between the MIS contacts could be 1/50th of the distancebetween the ohmic contacts (10).

The preferred materials for passivating the rear with the transparentpassivation or insulating lamina (11) are silicon nitride or siliconoxynitride (produced in plasma), or aluminum oxide or aluminumoxynitride, as the case may be. The manufacturing temperatures liebetween 300° C. and 600° C. The function of these layers on the rearside is, however, completely different to those on the front side. Inthe latter case, high positive charges must be present on the junctionto ensure that a highly conductive inversion layer (electron gas) isgenerated close under the top surface. In contrast, on the rear side thesurface recombination speed must be severely reduced; a highlyconductive inversion layer here tends to be adverse, since the minoritycharge carriers then flow to the ohmic contacts where they recombine andlose their utility. The rear silicon nitride layer (11) is produced athigher temperatures in comparison with the nitride layer (9) on thefront side. It is nevertheless advantageous to also enhance the positivecharge density in the rear nitride layer (11) by incorporating foreignions (especially alkali ions), since this does not reduce the density ofthe surface states but rather their electrical activity as centers ofrecombination. Thus in this manner, as well as reducing the hydrogenpassivation which occurs during nitride deposition or post-treatment byheat, one also reduces the surface recombination. In doing so, one alsoaccepts the inversion layer resulting from the high charge densities andthe sharply increased conductivity in said layer.

However, the present invention with the ohmic contacts (10) cut back byetching also very considerably reduces the adverse effect of theinversion layer in that, with constant spacing between the ohmiccontacts, the length of the inversion layer and thus their resistanceare both significantly increased bringing with it a sharp reduction inthe flow of minority charge carriers to the ohmic contacts. In thisrespect, this improved arrangement of the ohmic contacts (10) on therear permits further reduction in the recombination through higherinsulator charge densities, without having to accept the additionaldisadvantage relating to the inversion layer. This advantage alsoapplies to the solar cell illustrated in FIG. 1 with the elevated ohmiccontact grid on the front side. Aluminum oxide as insulating lamina (11)contains negative charges, which on p-doped silicon lead to a greaterconcentration of holes on the silicon surface. Advantageously theproblem with the inversion layer does not occur here at all, theelectrons as minority charge carriers being rejected from the rearsurface by the potential barrier.

If one does not wish to exploit the incident light on the rear surface,the option then exists of applying a highly reflective metal (e.g., Al,Ag), for instance, by vacuum deposition or cathode sputtering, on thetransparent insulating lamina (11) over the complete rear side. Theeffect is to double by reflection the path of the front incident lightin the silicon, and so increase the level of efficiency especially inthin, inexpensive solar silicon.

A solar cell (30) in accordance with the principles of the invention isshown in FIG. 3; said solar cell can be a conventional n⁺ p or else a p⁺n solar cell.

The n⁺ p solar cell (30) illustrated in the embodiment comprises asemiconductive substrate (12), a highly doped surface layer (13) (heren⁺), a non-areal ohmic contact (14) in grid form and a front-surfaceanti-reflection layer (15). Ohmic contacts (16), also not arranged overthe entire surface and preferably in ridge or grid form, are located onthe rear surface, as are passivation layers preferably in the form of asilicon oxide layer (17) and an insulating layer (18) doubling as ananti-reflection layer. Said insulating layer (18) is preferably made ofaluminum oxide or silicon nitride. The formation of an n⁺ p solar cell(30) on the rear surface, a solar cell designed for illumination fromboth sides is provided in a simple manner, with the additional advantagethat the long-wave heat radiation escapes from the cell (30) so that theoperating temperature drops (increase in open circuit voltage). Inaccordance with the invention, the ohmic contacts (16) are now arrangedin the form of fingers on elevations (25) effectively raised fromsurface (26) by silicon etching. The ohmic contacts (16) are covered bythe passivating layer (18).

Formation of the solar cell (30) in accordance with the inventionachieves the same advantages as with solar cell (20) in FIG. 2. However,there is a difference between the two cells (20) and (30) in the factthat solar cell (30) with a p-n junction incorporates high-temperatureprocesses, whereas the complete solar cell (20) is manufactured by usingsimple low-temperature processes. Both cells can exploit sunlightincident on the front surface as well as on the rear surface. Areflecting metal coating can be applied to the rear surface as anoption.

The features described in the aforegoing naturally also apply in thecase of solar cells with n-doped semiconductive substrates.

We claim:
 1. A solar cell comprising:a semiconductive substrate havingfirst and second opposed major surfaces in which minority and majoritycharge carriers are generated by radiation energy, said charge carriersbeing separable and so dischargeable by an electrical field, ohmiccontacts arranged at intervals upon said first semiconductive substratesurface, said contacts being interlinked with one another, and apassivation layer arranged at least between said ohmic contacts, andwherein the electrical field separating the minority and majority chargecarriers exists in the vicinity of said second semiconductive substratesurface positioned opposite said first semiconductive surface carryingsaid ohmic contacts, so that the majority charge carriers diffuse tosaid ohmic contacts which collect said charge carriers, said ohmiccontacts are arranged in first areas on said first semiconductivesubstrate surface, said first areas being elevated with respect tosecond areas which are located between said ohmic contacts, said ohmiccontacts are in direct contact with said semiconductive substratewithout shielding means, provided by doping said semiconductor substratein its first surface region, for shielding against the minority chargecarriers by a potential barrier, said second areas do not have apotential barrier against minority charge carriers provided by doping ofsaid semiconductor substrate in its first surface region, and said ohmiccontacts are covered by the passivation layer.
 2. A solar cell accordingto claim 1, wherein the electrical field separating the minority andmajority charge carriers is generated by MIS contacts formed on saidsecond substrate surface, and wherein said MIS contacts are covered withan insulating lamina containing electrical charges.
 3. A solar cellaccording to claim 1, wherein the distance separating said ohmiccontacts and said second surface of said semiconductive substrate isgreater than the diffusion length of the minority charge carriers.
 4. Asolar cell according to claim 1, wherein the distance separating theouter surface of said second areas and said second surface of saidsemiconductive substrate is smaller than the diffusion length of theminority charge carriers.
 5. A solar cell according to claim 1, whereinsaid first areas essentially determine the mechanical stability of saidsemiconductive substrate and have a trapezoidal, a rectangular or acurved cross-section.
 6. A solar cell according to claim 1, wherein saidfirst areas have peaks with said ohmic contacts arranged on said peaks,and said first areas exhibit a comb, grid or ring structure when viewedin plan.
 7. A solar cell according to claim 6, wherein said ringstructure is formed by concentrically arranged rings with radiallyrunning paths.
 8. A solar cell according to claim 1, wherein saidsemiconductive substrate is a single-crystalline (100)- or(110)-orientated silicon or polycrystalline silicon or compoundsemiconductor.
 9. A solar cell according to claim 1, wherein said firstand/or second areas are textured at least outside the regions of saidohmic contacts.
 10. A solar cell according to claim 1, wherein thedistance between said ohmic contacts is greater than the distancebetween said second areas and said second surface of said semiconductivesubstrate.
 11. A solar cell according to claim 10, wherein said ohmiccontacts, when viewed in plan, exhibit a finger-like structure, wherebythe spacing between the fingers lies between 1 mm and 5 mm and the widthof said fingers is from 50 μm to 300 μm.
 12. A solar cell according toclaim 1 in the form of a silicon nitride inversion layer solar cell witha plurality of spaced apart MIS contacts lying opposite said ohmiccontacts, and wherein the spacing between adjacent MIS contacts is aslittle as 1/50 of that between said ohmic contacts.
 13. A solar cellaccording to claim 12, wherein the distance separating said MIS contactsis between 50 μm and 1 mm, and that between said ohmic contacts isbetween 1 mm and 5 mm.
 14. A solar cell comprising:a semiconductivesubstrate having first and second opposed major surfaces in whichminority and majority charge carriers are generated by radiation energy,said charge carriers being separable and so dischargeable by anelectrical field, ohmic contacts arranged at intervals upon said firstsemiconductive substrate surface, said contacts being interlinked withone another, and a passivation layer arranged at least between saidohmic contacts, and wherein the electrical field separating the minorityand majority charge carriers exists in the vicinity of said secondsemiconductive substrate surface positioned opposite said firstsemiconductive surface carrying said ohmic contacts so that the majoritycharge carriers diffuse to said ohmic contacts which collect said chargecarriers, and said ohmic contacts are arranged in first areas on saidfirst semiconductive substrate surface, said first areas being elevatedwith respect to second areas which are located between said ohmiccontacts.
 15. A solar cell according to claim 14, wherein saidpassivation layer covers said ohmic contacts.
 16. A solar cell accordingto claim 14, wherein the electrical field separating the minority andmajority charge carriers is generated by MIS contacts formed on saidsecond substrate surface, and wherein said MIS contacts are covered withan insulating lamina containing electrical charges.
 17. A solar cellaccording to claim 14, wherein the distance separating said ohmiccontacts and said second surface of said semiconductive substrate isgreater than the diffusion length of the minority charge carriers.
 18. Asolar cell according to claim 14, wherein the distance separating theouter surface of said second areas and said second surface of saidsemiconductive substrate is smaller than the diffusion length of theminority charge carriers.
 19. A solar cell according to claim 14,wherein said first areas essentially determine the mechanical stabilityof said semiconductive substrate and have a trapezoidal, a rectangularor a curved cross-section.
 20. A solar cell according to claim 14,wherein said first areas have peaks with said ohmic contacts arranged onsaid peaks, and said first areas exhibit a comb, grid or ring structurewhen viewed in plan.
 21. A solar cell according to claim 20, whereinsaid ring structure is formed by concentrically arranged rings withradially running paths.
 22. A solar cell according to claim 14, whereinsaid semiconductive substrate is a single-crystalline (100)- or(110)-oriented silicon or polycrystalline silicon or compoundsemiconductor.
 23. A solar cell according to claim 14, wherein saidfirst and/or second areas are textured at least outside the regions ofsaid ohmic contacts.
 24. A solar cell according to claim 14, wherein thedistance between said ohmic contacts is greater than the distancebetween said second areas and said second surface of said semiconductivesubstrate.
 25. A solar cell according to claim 24, wherein said ohmiccontacts, when viewed in plan, exhibit a finger-like structure, wherebythe spacing between the fingers lies between 1 mm and 5 mm and the widthof said figures is from 50 μm to 300 μm.
 26. A solar cell according toclaim 14, in the form a silicon nitride inversion layer solar cell witha plurality of spaced apart MIS contacts, lying opposite said ohmiccontacts, and wherein the spacing between adjacent MIS contacts is aslittle as 1/50 of that between said ohmic contacts.
 27. A solar cellaccording to claim 26, wherein the distance separating said MIS contactsis between 50 μm and 1 mm, and that between said ohmic contacts isbetween 1 mm and 5 mm.